package store

import (
	"sync"
	"time"

	"tower/internal/model"
)

const defaultResolveAfter = 30 * time.Second

// Store is an in-memory IssueStore.
//
// Responsibilities (per PLAN.md):
// - Dedupe by Issue.ID
// - Track FirstSeen/LastSeen
// - Maintain State (Open/Acknowledged/Resolved)
// - Resolve issues only after resolveAfter duration of continuous absence
// - Acknowledgements are in-memory only (not persisted)
// - Safe for concurrent use
type Store struct {
	mu sync.RWMutex

	resolveAfter time.Duration

	// issues holds the latest known version of each issue keyed by stable ID.
	issues map[string]model.Issue

	// ack is an in-memory toggle keyed by issue ID.
	// If true and the issue is currently present, its state is Acknowledged.
	ack map[string]bool
}

// New returns a new Store.
// If resolveAfter <= 0, a default of 30s is used.
func New(resolveAfter time.Duration) *Store {
	if resolveAfter <= 0 {
		resolveAfter = defaultResolveAfter
	}
	return &Store{
		resolveAfter: resolveAfter,
		issues:       map[string]model.Issue{},
		ack:          map[string]bool{},
	}
}

// Upsert merges "currently true" issues for this tick.
//
// Incoming is deduped by Issue.ID; the first instance wins for non-timestamp fields.
// Timestamps/state are managed by the store.
func (s *Store) Upsert(now time.Time, incoming []model.Issue) {
	// Pre-dedupe without locking to keep lock hold times small.
	seen := make(map[string]model.Issue, len(incoming))
	for _, iss := range incoming {
		if iss.ID == "" {
			// Ignore invalid issues. ID is the stable dedupe key.
			continue
		}
		if _, ok := seen[iss.ID]; ok {
			continue
		}
		seen[iss.ID] = iss
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	for id, in := range seen {
		existing, ok := s.issues[id]
		if !ok || existing.State == model.StateResolved {
			// New issue (or a previously resolved one reappearing): start a new "episode".
			in.FirstSeen = now
			in.LastSeen = now
			in.State = model.StateOpen
			if s.ack[id] {
				in.State = model.StateAcknowledged
			}
			s.issues[id] = in
			continue
		}

		// Existing open/acked issue: update all fields from incoming, but preserve FirstSeen.
		in.FirstSeen = existing.FirstSeen
		in.LastSeen = now
		in.State = model.StateOpen
		if s.ack[id] {
			in.State = model.StateAcknowledged
		}
		s.issues[id] = in
	}

	// Update resolved state for issues not present this tick.
	s.applyResolutionsLocked(now, seen)
}

// Snapshot returns a point-in-time copy of all known issues with their states updated
// according to resolveAfter.
func (s *Store) Snapshot(now time.Time) []model.Issue {
	s.mu.Lock()
	defer s.mu.Unlock()

	// Apply resolutions based on time. We don't know which IDs are present "this tick"
	// from Snapshot alone, so we only resolve by absence window (LastSeen age).
	s.applyResolutionsLocked(now, nil)

	out := make([]model.Issue, 0, len(s.issues))
	for _, iss := range s.issues {
		out = append(out, deepCopyIssue(iss))
	}
	return out
}

// Acknowledge marks an issue acknowledged (in-memory only).
func (s *Store) Acknowledge(id string) {
	if id == "" {
		return
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	s.ack[id] = true
	iss, ok := s.issues[id]
	if !ok {
		return
	}
	if iss.State != model.StateResolved {
		iss.State = model.StateAcknowledged
		s.issues[id] = iss
	}
}

// Unacknowledge clears the acknowledgement toggle (in-memory only).
func (s *Store) Unacknowledge(id string) {
	if id == "" {
		return
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	delete(s.ack, id)
	iss, ok := s.issues[id]
	if !ok {
		return
	}
	if iss.State != model.StateResolved {
		iss.State = model.StateOpen
		s.issues[id] = iss
	}
}

func (s *Store) applyResolutionsLocked(now time.Time, present map[string]model.Issue) {
	for id, iss := range s.issues {
		// If caller provided a present set and the ID is present, it cannot be resolved.
		if present != nil {
			if _, ok := present[id]; ok {
				continue
			}
		}

		if iss.State == model.StateResolved {
			continue
		}
		if s.resolveAfter > 0 && now.Sub(iss.LastSeen) >= s.resolveAfter {
			iss.State = model.StateResolved
			s.issues[id] = iss
		}
	}
}

func deepCopyIssue(in model.Issue) model.Issue {
	out := in
	if in.Evidence != nil {
		m := make(map[string]string, len(in.Evidence))
		for k, v := range in.Evidence {
			m[k] = v
		}
		out.Evidence = m
	}
	return out
}